1. Field of the Invention
This invention relates to hydraulic turbines having a stationary bulb housing enclosing a generator unit and generally horizontal drive shaft. Particularly, this invention is directed to support structures for maintaining stationary positioning of the bulb housing in the hydraulic passageway.
2. Description of the Prior Art
In the prior art, hydraulic turbines having a stationary bulb housing submerged in flowing water are well known for the production of hydroelectric power. Such turbines commonly have a generally horizontal drive shaft affixed to a rotary runner equipped with turbine blades. The shaft terminates in a generator unit with the shaft and generator enclosed in the bulb housing. The hydraulic passageway surrounding the bulb housing is defined by a duct wall, commonly fabricated from plate steel or the like, lining a concrete foundation surrounding the bulb housing. Access passages are commonly provided through the foundation and hydraulic passage into the bulb housing to permit maintenance and inspection of the generator unit.
In the operation of the turbine, numerous forces act to displace the bulb housing. Specifically, the weight of the turbine, the buoyancy of the turbine, axial forces of flowing water, and the torque of the turbine all contribute to displace the turbine from a desired stationary and generally horizontal position. To secure the turbine, various support structures have been used. Examples of such prior art support structures are found in U.S. Pat. Nos. 3,393,324 to H. Hauser dated July 16, 1968; 4,151,970 to Bernhard dated May 1, 1979 and 4,191,504 to Haslinger dated Mar. 4, 1980.
One method known in the prior art of supporting a bulb turbine is to equip the turbine with a vertical support structure normal to the turbine drive shaft. In such a method, the bulb housing is equipped with a structural ring, or inner stay cone, axially displaced along the drive shaft between the generator and turbine runner. A second structural ring, or outer stay cone, of larger diameter is embedded within the duct wall and concrete foundation and is coplanar with the inner stay cone.
A singular vertical support member, or stay column, connects the inner and outer stay cones. The stay column is positioned along a line perpendicular to and intersecting the drive shaft. However, while the stay column connects the inner and outer stay cones, it cannot extend through the inner stay cone due to the axially positioned rotating drive shaft.
In addition to the stay column, the prior art method of support includes a support platform, or bottom pier, abutting the stay column away from the runner. The bottom pier is integral to the foundation and extends vertically into communication with the bottom of the bulb housing. An upper pier extends from the duct wall above the bulb housing down to the housing. The upper pier is commonly hollow thereby permitting ingress and egress to the interior of the bulb.
It is known to be desirable to construct the piers and stay columns of a dimension, as small as possible, to reduce the amount of volume in the hydraulic passageway occupied by the piers and stay columns. Additionally, the stay columns and abutting piers are so constructed so in horizontal cross section they form a teardrop shape tapered toward the runner thereby minimizing resistance to the hydraulic flow about the bulb toward the turbine blades.
While the above-described prior art support structure has been satisfactory in the past, the current demand for hydroelectric power has precipitated the demand for larger bulb turbines. As the size of the bulb turbine increases, the aforementioned forces acting to displace the desired stationary positioning of the bulb increase. Additionally, larger turbines require larger hydraulic passages resulting in an increased area of unsupported foundation in overlying relation to the bulb turbine.
The result of the increased forces, together with the weight of the overlying foundation transmitted to the bulb through the pier and stay column above the bulb, is an intolerable compressing and twisting force upon the inner stay cone in the bulb housing. These forces tend to deform the inner stay cone and urge the turbine out of its desired stationary position.
It has been suggested to accommodate the increased force by simply increasing the dimensions of the stay column and piers. However, this suggestion is unsatisfactory for at least two reasons. The increased dimensions would reduce the volume of water that could pass to the turbine blades thereby reducing turbine efficiency. Additionally, the larger dimension would not diminish, but indeed would increase, the compression forces acting on the inner stay cone.
Applicant has determined the larger forces attendent with larger bulb turbines can be accommodated without an increase in the dimensions of the piers and stay column by dividing the piers and column in half and placing the support structure on both sides of the drive shaft. This configuration permits passing twin-stay columns through the inner stay cone. By affixing the inner stay cone to the stay columns at the location of intersection, the inner stay cone acts as a structural cross member joining the twin-stay columns thereby eliminating the above-described compression of the inner stay cone. Additionally, this design retains the desired minimum dimensions of the support structure and the hydraulic teardrop shape of the support structure thereby permitting the relatively uninhibited flow of water about the bulb housing to the turbine blades.
The object of the present invention is to provide a structural support for a hydraulic turbine which relieves compression forces acting upon the turbine bulb housing.
It is a further object of the present invention to provide a structural support for a hydraulic turbine which requires a minimum of interference with the volume of water passing the bulb housing and which permits a hydraulic shape thereby minimizing flow impedence about the support structure.